Process of lead cladding using molten lead



United States Patent 3,244,553 PROCESS OF LEAD CLADDENG USING MOLTEN LEAD Victor E. Knapp, Roslyn, N.Y., and Neil F. Ritchey,

Chester County, Pa., assignors to Knapp Miils Incorpforited, Long Island City, N.Y., a corporation of New or No Drawing. Original application Dec. 22, 1959, Ser. No. 861,198. Divided and this application Jan. 11, 1965, Ser. No. 440,042

4 Claims. (Cl. 11771) This application is a division of application Serial No. 861,198 filed Dec. 22, 1959 now Patent No. 3,167,858 dated Feb. 2, 1965 which is a continuation-in-part of our application No. 686,876 filed Sept. 30, 1957, and now abandoned.

The present invention relates to the cladding of lead on sheets of copper, aluminum, iron and their alloys. It has been found that these metals can be cladded with lead so as to form a bonded sheet which is useful for shielding against the harmful effects of radiation or corrosion. In the following description of the invention, the particular metal which is to be clad will be called the basic metal, with the understanding that it may either be steel, copper, aluminum, or alloys thereof.

Lead cladded metal structures are becoming increasingly important in radiation shielding. Until the present invention, no completely satisfactory method has been evolved to effect the bonding of lead to these metals in a wide range of thicknesses and by a reliable and relatively easily per-formed commercially practical method.

According to the present invention, a method is disclosed which permits the creation of a strong metallurgical bond between the lead and a basic metal so as to form lead clad metal sheets or plates wherein the lead and the basic meta-l are so tightly bonded together that the sheets or plates may be bent, cut, shaped, or otherwise handled without any separation of the two metals.

Accordingly, an object of the present invention is to provide an improved method of cladding a basic metal with lead.

Another object of the present invention is to provide an improved lead clad basic metal.

Another object of the present invention is to provide an improved method of metallurgically bonding a basic metal and lead together.

Another object of the present invention is to provide a .practical and reliable method of bonding lead to a basic metal which is suitable for commercial use.

Other and further objects of the invention will be obvious upon an understanding of the illustrative embodiment about to be described, or will be indicated in the appended claims, and various advantages not referred to herein will occur to one skilled in the art upon employment of the invention in practice.

The first step in the process comprises the coating or plating with nickel of the basic metal surface which is to be clad with lead. The coating of the basic metal with the nickel may be accomplished by any of the known types of nickelplate, such as elecrtoplating or chemical plating.

A preferred chemical process which provides a bond between the nickel and the basic metal is accomplished by a controlled catalytic reduction of nickel in a plating bath. In such a bath, the basic metal parts are immersed in a hot solution containing a chemical reducing agent, such as sodium hypophospite and a buffered solution of nickel salt, such as nickel chloride.

Suitable solutions for such a chemical plating of nickel have also been disclosed in US. Patents Nos. 2,658,841 and 2,658,842 which issued to Gutzeit and Kreig, Patent No. 2,694,017 which issued to Rischan and Kreig, and Patent N 0. 2,694,019 which issued to Gutzeit. The plate solutions which were disclosed in these patents may be applied by the process described more completely in Patents No. 2,658,839 which issued to P. Tallmey, et al., No. 2,717,218 which issued to P. Tallmey et al., No. 2,762,723 which issued to Tallmey and Gutzeit, and No. 2,766,138 which issued to Paul Tallmey. These patents disclose processes for depositing nickel on the basic metals. The coatings which result from these processes are not in all cases pure nickel. They may, for example, include phosphides. The presence of these additional elements in the coatings have been found to have no adverse affect upon the lead cladding process and in the case of the phosphides, their presence in the nickel coats have been found to provide improved adherence between the lead and the basic metal for reasons which at this time are not clearly understood.

The nickel coating is preferably thicker than .0005. A coating thickness of .001 has provided a satisfactory bond.

After the basic metal has been nickel-plated, the nickel is tinned with a mixture of lead and tin or antimony. A preferred tinning mixture comprises about 41 percent lead and 59 percent tin which is melted to permit dipping of the nickel-plated surface into the tinning mixture. The melting point for the 41 percent lead and the 59 percent tin mixture is about 360 F. The basic metal is preferably fiuxed with one of the suitably known fluxes for the bonding of tin to the particular basic metal prior to the tinning.

The tinning of the basic metal having been completed, the metal is ready to receive the lead to which it is to be bonded. Several methods may be utilized to bring the lead in contact with the tinned surface of the basic metal. Each of them makes use of the principle that the lead-tin eutectic coating must first be melted before the lead metal will adhere to it.

In the lead burning method, the lead may be hand deposited on the basic metal by simply burning a bar of lead over the basic metal. Thus the lead melts and flows by gravity so that it spreads over the tinned basic metal surface. The burning may be accomplished with any heating implement capable or furnishing a sufficiently high temperature to melt the lead, as with a torch operated with hydrogen or propane gas, for example.

As the lead is spreading over the tinned surface, a workman plays over the surface with a torch, and fuses the lead into the tinned surface. The high temperature of the lead and the heat from the torch are more than is necessary to heat the eutectic coating so that it becomes largely or completely liquified. The above procedure may be continued until the entire surface has been coated with lead. Additional layers of lead may be deposited in a similar fashion to increase the overall thickness by repeating the same operation with new quantities of lead metal,

Another method of bringing the lead into contact with the basic metal surface is called the pour-bonding method. In this method, after the basic metal has been tinned, as above, it is preheated to about 400 F. Meanwhile, lead metal has been heated to a temperature of 700 to 750 F., so that it is now entirely molten. The lead is then simply poured over the tinned basic metal surface to any thickness required. As the molten lead comes into contact with the tinned surface of the basic metal, it forms a homogenous mass with the eutectic coating which has melted under the heat applied so that an excellent bond with the basic metal is produced.

The lead coating may be applied to the base metal by extrusion. In this method the base metal in the form of rods or tubes is first nickel-plated and tinned and the lead and the base metal tubes or rods are fed through heated extrusion dies to bond a coating of lead to the outer surface of the tubes or rods.

Finally, the lead may also be brought into contact with the tinned basic metal surface in solid form, usually as sheets, by what is called the roller or platens pressure method. In this method, after the basic metal surface has been nickel-plated and tinned, the surface of the load. which is to be bonded to the basic metal is cleaned to remove lead oxide by scraping or other suitable cleaning methods and the cleaned basic metal surface is also tinned. As the basic metal must be heated for the bonding, the basic metal slab is preferably heated prior to the tinning. The bonding temperatures are slightly above the melting point of tin. Lead eutectic alloy is used to tin both the lead and the basic metal so that the lead is heated 3040 F. above the 360 F. melting point for the tin-lead alloy. The lead is now tinned. A preferred method of tinning the lead is by hand wiping using an oxygen-hydrogen torch to apply heat as needed.

The basic metal and lead sheets or plates are bonded together under pressure by means of either platens or rollers. Preferably, the platens or rollers which serve to press the lead and the basic metal are heated to the bonding temperature so that the bonding temperature will be maintained during the required pressure period. The platens, for instance, may be heated to about 400 F. prior to the insertion of the lead. and the basic metal therebetween. After the lead has been tinned, it is reheated, if necessary, to about 400 F. and the nickel coated and tinned face of the basic metal is placed against the tinned surface of the lead. The basic metal and lead are now pressed between the platens or rollers, as the case may be.

Sufficient pressure is applied to insure a tight engagement of the two tinned surfaces. Where aluminum has been used as a basic metal, a pressure of about 15 psi. has been found to be satisfactory. The pressure is maintained for a sufficient period to insure the formation of the bond. For instance, with aluminum, when the preferred pressure of 15 p.s.i. is used, a pressure period of two minutes is preferred. At the end of this period, the lead and basic metal are cooled while still under pressure to solidify the interface. This may be done by a suitabl water spray. Thereafter, the pressure is released to permit the removal of the bonded metals.

In the particular case of bonding aluminum to lead, where the aluminum has been hardened or otherwise treated for increased strength, it is necessary to limit the heating of the aluminum during the bonding to an amount which will not cause over-aging of the heat treated aluminum. It is well known that where heat treated alloys are subjected to heat, a time is reached when the strengths of the aluminum alloys begin to decrease. This is known as over-aging. It is desirable to keep the total time for the bonding process for aluminum alloys below the overaging range. The aluminum or the aluminum alloy is heated twice in the above-described process to a temperature of about 400 F. The first heating is in the tinning Maximum Time Before Over-aging Temperature,

Aluminum Alloy Degrees F.

15 sec. 30 see.

3 min. 10 min. 20 hours. 15 sec. 30 sec.

2 min.

5 min. 30 min.

2024-186 and 606l-T6 It will be seen that the present invention provides an improved method for metallurgically bonding lead to sheets or plates of a basic metal which may be copper, aluminum, iron or their alloys. The method of the present invention provides an improved lead clad basic metal in which an extremely tight bond is formed between the basic metal and the lead. The finished bonded sheets may be subjected to additional manufacturing processes such as bonding, cutting, and shaping, without a failure of the bond. The process is relatively simple and is reliable so that it is suitable for commercial usage on a large scale to provide numerous lead cladded metal products in the constantly growing market for such products. It has been found that the lead clad basic metal as formed by the process of the present invention in many cases has a tensile strength which is greater than would be expected from the combined strengths of the lead and basic metal and that there is an unexpected and important increase in the strength of the finished product which results from the practice of the cladding process of the invention.

As various changes may be made in the form, construction, and arrangement of the parts herein without departing from the spirit and scope of the invention and without sacrificing any of its advantages, it is to be understood that all matter herein is to be interpreted as illustrative and not in a limiting sense.

Similarly, it is to be understood that the mention of any metal is intended to include any of its alloys as well. Thus, iron includes steel or any of the other alloys of iron.

Having thus described our invention, we claim:

1. The process of forming and metallurgically bonding a relatively thick layer of lead on a basic metal included in the group consistiing of copper, aluminum, iron and their alloys, which comprises the steps of coating a surface of the basic metal with a relatively thin nickel layer, applying a relatively thin tin-lead eutectic layer to the nickel layer, at least partially melting the said eutectic coating, building up a relatively thick layer of lead in hot molten form above the surface of said eutectic coating whereby the heated lead and the partially melted tinlead eutectic coating bond together, and thereafter cooling the bonded metals.

2. The process as claimed in claim 1 in which the nickel coating of the basic metal comprises a controlled catalytic reduction in a hot bath comprising a chemical reducing agent and a nickel salt.

3. The process as claimed in claim 2 in which the nickel salt comprises nickel chloride and the chemical reducing agent comprises sodium hypophosphite whereby the nickel layer comprises about 8-12 percent phosphorus and 91- 88 percent nickel.

4. The process as claimed in claim 2 in which the chemical reducing agent comprises a hypophosphite, wherein the ratio between nickel ions and hypophosphite ions in said bath expressed in molar concentrations is Within the range 0.25 to 0.60, wherein the absolute con- 'centration of hypophosphite ions in said bath expressed in mole per liter is within the range 0.15 to 0.35, and wherein the initial pH of said bath is within the approximate range 4.5 to 5.6.

References Cited by the Examiner UNITED STATES PATENTS 440,952 11/1890 Land 29-503 X 1,079,035 11/ 1913 Tebetts 29-197 1,280,908 10/1918 Wales et a1 29-1966 X 1,975,818 10/1934 Work 117-1 1,996,657 4/ 1935 Shannon 29492 2,174,733 10/1939 Chace 29-1966 X 2,428,033 9/1947 Nachtman 29-1966 X 2,694,017 11/ 1954 Reschan et 211.

5/1956 Richand 29-197 6/1957 Antel et al. 29-504 2/ 1958 Erickson 29-197 X 5/1958 Dalton 117-71 X 6/1958 Storcheim 29-197 X 7/1958 Robinson 207-103 X 5/1959 Fike et al. 29-197 X 5/ 1961 Drummond 29-470 FOREIGN PATENTS 6/ 1949 Great Britain.

OTHER REFERENCES Aluminum Soldering, Supplement to the Journal of the American Welding Society, September 1940, pp.

15 szo-s and 321-s.

Burns and Bnadley: Protective Coatings for Metals, Reinhold Pub. Corp., 2nd ed., 1955, pp. 246, 247.

RICHARD D. NEVIUS, Primary Examiner.

JOSEPH B. SPENCER, R. S. KENDALL, Examiners. 

1. THE PROCESS OF FORMING AND METALLURGICALLY BONDING A RELATIVELY THICK LAYER OF LEAD ON A BASIC METAL INCLUDED IN THE GROUP CONSISTING OF COPPER, ALUMINUM, IRON AND THEIR ALLOYS, WHICH COMPRISES THE STEPS OF COATING A SURFACE OF THE BASIC METAL WITH A RELATIVELY THIN NICKEL LAYER, APPLYING A RELATIVELY THIN TIN-LEAD EUTECTIC LAYER TO THE NICKEL LAYER, AT LEAST PARTIALLY MELTING THE SAID EUTECTIC COATING, BUILDING UP A RELATIVELY THICK LAYER OF LEAD IN HOT MOLTEN FORM ABOVE THE SURFACE OF SAID EUTECTIC COATING WHEREBY THE HEATED LEAD AND THE PARTIALLY MELTED TINLEAD EUTECTIC COATING BOND TOGETHER, AND THEREAFTER COOLING THE BONDED METALS. 